Inductor built-in substrate and method for manufacturing inductor built-in substrate

ABSTRACT

An inductor built-in substrate includes a core substrate having an opening and a first through hole formed therein, a magnetic resin filling the opening of the core substrate and having a second through hole formed therein, a first through-hole conductor including a metal film formed in the first through hole of the core substrate, and a second through-hole conductor including a metal film formed in the second through hole of the magnetic resin. The magnetic resin includes a resin material and magnetic particles such that the metal film of the second through-hole conductor is in contact with the magnetic particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims the benefit of priority to Japanese Patent Application No. 2019-212533, filed Nov. 25, 2019, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an inductor built-in substrate that has an inductor built therein and a method for manufacturing the inductor built-in substrate.

Description of Background Art

Japanese Patent Application Laid-Open Publication No. 2016-197624 describes a method for manufacturing an inductor component built in a wiring substrate. In Japanese Patent Application Laid-Open Publication No. 2016-197624, a magnetic material is accommodated inside a resin layer, through-hole conductors are provided in the resin layer, and the through-hole conductors are prevented from being in contact with the magnetic material. The entire contents of this publication are incorporated herein by reference.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an inductor built-in substrate includes a core substrate having an opening and a first through hole formed therein, a magnetic resin filling the opening of the core substrate and having a second through hole formed therein, a first through-hole conductor including a metal film formed in the first through hole of the core substrate, and a second through-hole conductor including a metal film formed in the second through hole of the magnetic resin. The magnetic resin includes a resin material and magnetic particles such that the metal film of the second through-hole conductor is in contact with the magnetic particles.

According to another aspect of the present invention, a method for manufacturing an inductor built-in substrate includes forming an opening in an insulating base material, filling a magnetic resin including magnetic particles in the opening formed in the insulating base material, curing the magnetic resin filled in the opening of the insulating base material, forming a first through hole in the insulating base material, forming a second through hole in the magnetic resin filled in the opening of the insulating base material, and forming a plating film in the first through hole formed in the insulating base material and in the second through hole formed in the magnetic resin filled in the opening of the insulating base material. The forming of the second through hole in the magnetic resin includes cutting surfaces of the magnetic particles in the magnetic resin such that cut surfaces of the magnetic particles are exposed on a wall surface of the second through hole.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1A is a cross-sectional view of an inductor built-in substrate according to an embodiment of the present invention;

FIG. 1B is a plan view of through-hole lands;

FIG. 1C is an enlarged view of a core substrate of the inductor built-in substrate;

FIGS. 2A-2D are process diagrams illustrating a method for manufacturing an inductor built-in substrate according to an embodiment of the present invention;

FIGS. 3A-3D are process diagrams illustrating the method for manufacturing an inductor built-in substrate according to the embodiment;

FIGS. 4A-4C are process diagrams illustrating the method for manufacturing an inductor built-in substrate according to the embodiment; and

FIG. 5 is a photomicrograph of a cut surface of a first electroless plating film and a first electrolytic plating film on a second through hole.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.

FIG. 1A illustrates a cross-sectional view of an inductor built-in substrate 10 of an embodiment that has an inductor built therein. The inductor built-in substrate 10 has a core substrate 30 that is formed to include: an insulating base material 20 that has a first surface (F) and a second surface (S) on an opposite side with respect to the first surface (F); a first conductor layer (conductor circuit) (58F) on the first surface (F) of the insulating base material; a second conductor layer (58S) on the second surface (S) of the insulating base material; and through-hole conductors 36 that connect the first conductor layer (58F) and the second conductor layer (58S) to each other. The core substrate 30 has a first surface (F) and a second surface (S) on an opposite side with respect to the first surface (F). The first surface (F) of the core substrate 30 and the first surface (F) of the insulating base material 20 are the same surface, and the second surface (S) of the core substrate 30 and the second surface (S) of the insulating base material 20 are the same surface. The insulating base material 20 is formed of a resin such as an epoxy resin and a core material 14 such as a glass cloth for reinforcement. The insulating base material 20 may further contain inorganic particles such as silica particles.

The inductor built-in substrate 10 further has an upper side build-up layer (450F) formed on the first surface (F) of the core substrate 30. The upper side build-up layer (450F) includes: an insulating layer (450A) formed on the first surface (F) of the core substrate 30; a conductor layer (458A) formed on the insulating layer (450A); and via conductors (460A) penetrating the insulating layer (450A) and connecting the first conductor layer (58F) and the conductor layer (458A) to each other. The upper side build-up layer (450F) further includes: an insulating layer (450C) formed on the insulating layer (450A) and the conductor layer (458A); a conductor layer (458C) formed on the insulating layer (450C); and via conductors (460C) penetrating the insulating layer (450C) and connecting the conductor layer (458A) and the via conductors (460A) to the conductor layer (458C).

The inductor built-in substrate 10 further has a lower side build-up layer (450S) formed on the second surface (S) of the core substrate 30. The lower side build-up layer (450S) includes: an insulating layer (450B) formed on the second surface (S) of the core substrate 30; a conductor layer (458B) formed on the insulating layer (450B); and via conductors (460B) penetrating the insulating layer (450B) and connecting the second conductor layer (58S) and the conductor layer (458B) to each other. The lower side build-up layer (450S) further includes: an insulating layer (450D) formed on the insulating layer (450B) and the conductor layer (458B); a conductor layer (458D) formed on the insulating layer (450D); and via conductors (460D) penetrating the insulating layer (450D) and connecting the conductor layer (458B) and the via conductors (460B) to the conductor layer (458D).

The inductor built-in substrate of the embodiment further includes a solder resist layer (470F) having openings (471F) formed on the upper side build-up layer (450F) and a solder resist layer (470S) having openings (471S) formed on the lower side build-up layer (450S).

Upper surfaces of the conductor layers (458C, 458D) or the via conductors (460C, 460D) exposed from the openings (471F, 471S) of the solder resist layers (470F, 470S) function as pads. A protective film 472 formed of Ni/Au, Ni/Pd/Au, Pd/Au, or OSP is formed on each of the pads. Solder bumps (476F, 476S) are respectively formed on the protective films. An IC chip (not illustrated in the drawings) is mounted on the inductor built-in substrate 10 via the solder bumps (476F) formed on the upper side build-up layer (450F). The inductor built-in substrate 10 is mounted on a motherboard (not illustrated in the drawings) via the solder bumps (476S) that are formed on the lower side build-up layer (450S).

FIG. 1C illustrates an enlarged view of a portion of the core substrate 30 in FIG. 1A. In the core substrate 30, the through-hole conductors 36 connecting the first conductor layer (58F) and the second conductor layer (58S) to each other include first through-hole conductors (36A) that are respectively formed in first through holes (20 a) penetrating the core substrate 30 and second through-hole conductors (36B) that are respectively formed in second through holes (18 b) of a magnetic resin 18 filled in openings (20 b) of the core substrate 30. A diameter (da) of each of the first through holes (20 a) and a diameter (db) of each of the second through holes (18 b) are substantially equal to each other. A resin filler 16 is filled inside the first through-hole conductors (36A) and the second through-hole conductors (36B), and through-hole lands (58FR) are formed of cover plating. The through-hole lands (58FR) include first through-hole lands (58FRA) respectively formed on the first through-hole conductors (36A) and second through-hole lands (58FRB) respectively formed on the second through-hole conductors (36B). The magnetic resin 18 does not contain a core material.

FIG. 1B is a plan view of a first through-hole land (58FRA) formed on a first through-hole conductor (36A) and a second through-hole land (58FRB) formed on a second through-hole conductor (36B). The first through-hole land (58FRA) is concentrically formed with the first through-hole conductor (36A), and the second through-hole land (58FRB) is concentrically formed with the second through-hole conductor (36B). A diameter (Da) of the first through-hole land (58FRA) and a diameter (Db) of the second through-hole land (58FRB) are substantially equal to each other. The first through-hole land (58FRA) and the second through-hole land (58FRB) are connected to each other by the first conductor layer (circuit pattern) (58F). The diameter (Db) of the second through-hole land (58FRB) is smaller than a diameter (DB) of each of the openings (20 b) in which the magnetic resin 18 is filled. That is, the second through-hole land (58FRB) does not spread from the magnetic resin 18 to the insulating base material 20.

The magnetic resin 18 contains an iron oxide filler (magnetic particles) and a resin such as an epoxy resin. Examples of the magnetic particles include iron oxide fillers such as iron (III) oxide particles. A content of the iron oxide filler in the magnetic resin is preferably 60-90% by weight. From a point of view that the content of the iron oxide filler can be increased and magnetic permeability and heat conductivity can be increased, particle sizes of the iron oxide filler are desirably non-uniform. The iron oxide filler desirably has an average particle size of 5 μm-45 μm. As will be described later, a cut surface of the iron oxide filler is formed on a side wall of each of the second through holes (18 b) of the magnetic resin 18. When the average particle size is less than 5 μm, the iron oxide filler is likely to fall off the side wall. When the average particle size exceeds 45 μm, it is difficult to cut the iron oxide filler.

As illustrated in FIG. 1C, a first through-hole conductor (36A) formed in a first through hole (20 a) penetrating the core substrate 30 is in contact with the first through hole (20 a). The first through-hole conductor (36A) includes a first electroless plating film 32 on the first through hole (20 a), and a first electrolytic plating film 34 on the first electroless plating film 32. A second through-hole conductor (36B) formed in a second through hole (18 b) penetrating the magnetic resin 18 is in contact with the second through hole (18 b). The second through-hole conductor (36B) includes a first electroless plating film 32 on the second through hole (18 b), and a first electrolytic plating film 34 on the first electroless plating film 32.

FIG. 5 is a photomicrograph of a cut surface of the first electroless plating film 32 and the first electrolytic plating film 34 on the second through hole (18 b). Cut surfaces of magnetic particles are exposed on the surface of the second through hole (18 b), and the first electroless plating film 32 forming the second through-hole conductor (36B) is formed so as to be in contact with the cut surfaces of the magnetic particles.

In the inductor built-in substrate 10 of the embodiment, since there are no vacancies formed by missing magnetic particles on side surfaces of the second through holes (18 b), there is no defect in the formation of the metal films (the first electroless plating film 32 and the first electrolytic plating film 34) due to vacancies, and there is no disconnection in the second through-hole conductors (36B) due to a defect in the formation of the metal films. Therefore, reliability of the second through-hole conductors (36B) can be increased. Further, since the second through-hole conductors (36B) can have a uniform film thickness, electrical characteristics can be improved.

The first through-hole lands (58FRA) and the first conductor layer (58F) on the insulating base material 20 are each formed of a copper foil 22 as a lowermost layer, the first electroless plating film 32 on the copper foil 22, the first electrolytic plating film 34 on the first electroless plating film 32, a second electroless plating film 35 on the first electrolytic plating film 34, and a second electrolytic plating film 37 on the second electroless plating film 35. The second through-hole lands (58FRB) and the first conductor layer (58F) on the magnetic resin 18 are each formed of the first electroless plating film 32 as a lowermost layer, the first electrolytic plating film 34 on the first electroless plating film 32, the second electroless plating film 35 on the first electrolytic plating film 34, and the second electrolytic plating film 37 on the second electroless plating film 35.

In the core substrate 30 of the embodiment, the first conductor layer (58F) (connection pattern (58FL)) and the second conductor layer (58S) (connection pattern (58SL)) which are connected to each other via the second through-hole conductors (36B) formed in the magnetic resin 18 illustrated in FIG. 1A are formed in a helical shape (a spiral shape along an axis in a direction parallel to the front and back surfaces of the core substrate), and together with the second through-hole conductors (36B) form an inductor 59.

In the inductor built-in substrate 10 of the embodiment, the first conductor layer (58F) and the second conductor layer (58S) are formed on the surfaces of the core substrate 30, and the second through-hole conductors (36B) connecting the first conductor layer (58F) and the second conductor layer (58S) to each other are directly formed in the second through holes (18 b) penetrating the magnetic resin 18. Therefore, a ratio of a magnetic material in the inductor built-in substrate 10 is increased and an inductance can be increased.

Method for Manufacturing Inductor Built-in Substrate

A method for manufacturing an inductor built-in substrate according to an embodiment of the present invention is illustrated in FIGS. 2A-4C.

A copper-clad laminated plate formed by laminating the copper foil 22 on both sides of the insulating base material 20 is prepared (FIG. 2A). The openings (20 b) for filling the magnetic resin therein are formed in the insulating base material 20 (FIG. 2B). A resin paste (18 a) containing an iron oxide filler (magnetic particles) in an amount of 60-90% by weight and an epoxy resin is vacuum-printed in the openings (20 b) (FIG. 2C). The surfaces of the insulating base material 20 are polished, and surfaces of the resin paste (18α) are flattened (FIG. 2D).

The resin paste is heated to cause the resin contained therein to crosslink and become cured, and thereby, the magnetic resin 18 is formed (FIG. 3A). Here, the heating is performed at 150° C.-190° C. for 1 hour. By mechanical drilling, the first through holes (20 a) are formed in the insulating base material 20, and the second through holes (18 b) are formed in the magnetic resin 18 (FIG. 3B). As illustrated in FIG. 5, to expose cut surfaces of magnetic particles on side surfaces of the second through holes (18 b), a mechanical drill is used that has one chip discharge groove on a body thereof, the chip discharge groove having a twist angle of 30-50 degrees. A drill of which a chip discharge groove has a twist angle of 30-50 degrees is excellent in chip discharge and is less likely to retain heat. Here, when a drill of which a chip discharge groove has a twist angle of less than 30 degrees or more than 50 degrees is used, it is difficult to discharge chips. The iron oxide filler particles are likely to fall off the side walls, and recesses formed by the falling of the iron oxide filler particles are likely to be formed on the side surfaces of the second through holes (18 b).

Desmear is performed without using an acidic agent. For example, smears (residues) during drilling in the first through holes (20 a) and in the second through holes (18 b) are removed by high-pressure water washing. When desmear is performed using an acidic agent, there is a risk that the acidic agent may cause the iron oxide filler particles contained in the magnetic resin 18 to fall off in a process of swelling and peeling off the resin, and thus, high-pressure water washing is performed here. After that, the processing smears in the first through holes (20 a) and the second through holes (18 b) are further removed by a dry desmear treatment using O2 plasma or the like. Here, the processed smears are removed by high-pressure water washing and a dry desmear treatment. However, it is also possible to remove the smears in the first through holes (20 a) and the second through holes (18 b) using, for example, an alkaline chemical solution or the like that does not alter the nature of the iron oxide filler. Further, it is also possible to perform formation and perform desmear using an acidic agent for the first through holes (20 a), and then perform formation and perform desmear by high-pressure water washing or the like without using an acidic agent for the second through holes (18 b).

In the manufacturing method of the embodiment, the smear removal treatment in the first through holes (20 a) of the insulating base material 20 and the second through holes (18 b) of the magnetic resin 18 is performed at the same time. Therefore, it is not necessary to provide a shield layer for protecting the magnetic resin, and the inductor built-in substrate can be easily manufactured.

On the surfaces of the insulating base material 20 and the magnetic resin 18 and on the surfaces of the first through holes (20 a) and the second through holes (18 b), the first electroless plating film 32 is formed by an electroless plating treatment, and the first electrolytic plating film 34 is formed by an electrolytic plating treatment. By the first electroless plating film 32 and the first electrolytic plating film 34, the first through-hole conductors (36A) are formed in the first through holes (20 a) and the second through-hole conductors (36B) are formed in the second through holes (18 b) (FIG. 3C).

The resin filler 16 is filled inside the first through-hole conductors (36A) formed in the first through holes (20 a) and inside the second through-hole conductors (36B) formed in the second through holes (18 b), and the surfaces of the insulating base material 20 are polished (FIG. 3D). The second electroless plating film 35 is formed on the first electrolytic plating film 34 and on the exposed surface of the resin filler 16 by electroless plating, and the second electrolytic plating film 37 is formed on the second electroless plating film 35 (FIG. 4A). An etching resist 54 of a predetermined pattern is formed on the second electrolytic plating film 37 (FIG. 4B).

The second electrolytic plating film 37, the second electroless plating film 35, the first electrolytic plating film 34, the first electroless plating film 32, and the copper foil 22 exposed from the etching resist 54 are removed, and after that, the etching resist is removed, and the first conductor layer (58F) and the second conductor layer (58S) are formed and the core substrate 30 is completed (FIG. 4C). The first conductor layer (58F) and the second conductor layer (58S) on the insulating base material 20, and the first through-hole lands (58FRA) on the first surface (F) side and the first through-hole lands (58SRA) on the second surface (S) side of the first through-hole conductors (36A) are each formed of the copper foil 22 as a lowermost layer, the first electroless plating film 32 on the copper foil 22, the first electrolytic plating film 34 on the first electroless plating film 32, the second electroless plating film 35 on the first electrolytic plating film 34, and the second electrolytic plating film 37 on the second electroless plating film 35. The first conductor layer (58F) and the second conductor layer (58S) on the magnetic resin 18, and the second through-hole lands (58FRB) on the first surface (F) side and the second through-hole lands (58SRB) on the second surface (S) side of the second through-hole conductors (36B) are each formed of the first electroless plating film 32, the first electrolytic plating film 34 on the first electroless plating film 32, the second electroless plating film 35 on the first electrolytic plating film 34, and the second electrolytic plating film 37 on the second electroless plating film 35.

The upper side build-up layer (450F), the lower side build-up layer (450S), the solder resist layers (470F, 470S), and the solder bumps (476F, 476S) are formed on the core substrate 30 using known manufacturing methods (FIG. 1A).

In the method for manufacturing the inductor built-in substrate of the embodiment, the second through-hole conductors (36B) formed of the first electroless plating film 32 and the first electrolytic plating film 34 are formed in the second through holes (18 b) of the magnetic resin 18. Therefore, the volume of the magnetic resin 18 of the inductor built-in substrate 10 can be increased, and the inductance can be increased.

In Japanese Patent Application Laid-Open Publication No. 2016-197624, since the through-hole conductors are formed in the resin layer, it is thought that a ratio of the magnetic material with respect to a size of the inductor component is low and it is difficult to increase an inductance.

An inductor built-in substrate according to an embodiment of the present invention is small in size and has a large inductance and through-hole conductors that have high reliability, and according to another embodiment of the present invention is a method for manufacturing the inductor built-in substrate.

An inductor built-in substrate according to an embodiment of the present invention includes: a core substrate in which an opening and a first through hole are formed; a magnetic resin that is filled in the opening and has a second through hole; a first through-hole conductor that is formed of a metal film formed in the first through hole; and a second through-hole conductor that is formed of a metal film formed in the second through hole. The magnetic resin contains magnetic particles and a resin. The metal film of the second through-hole conductor is in contact with the magnetic particles.

A method for manufacturing an inductor built-in substrate according to an embodiment of the present invention includes: forming an opening in an insulating base material; filling a magnetic resin containing magnetic particles in the opening; curing the magnetic resin; forming a first through hole in the insulating base material; forming a second through hole in the magnetic resin; and forming a plating film in the first through hole and in the second through hole. When the second through hole is formed in the magnetic resin, cut surfaces of the magnetic particles are exposed on a wall surface of the second through hole.

In an inductor built-in substrate according to an embodiment of the present invention, the second through-hole conductor formed of a metal film is directly formed in the second through hole of the magnetic resin. Therefore, a volume of the magnetic resin of an inductor component can be increased, and an inductance can be increased. The metal film of the second through-hole conductor is in contact with the cut surfaces of the magnetic particles. That is, since there are no vacancies formed by missing magnetic particles on the side surface of the second through hole, there is no defect in the formation of the metal film due to vacancies, and there is no disconnection in the second through-hole conductor due to a defect in the formation of the metal film. Therefore, reliability of the second through-hole conductor can be increased.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

What is claimed is:
 1. An inductor built-in substrate, comprising: a core substrate having an opening and a first through hole formed therein; a magnetic resin filling the opening of the core substrate and having a second through hole formed therein; a first through-hole conductor comprising a metal film formed in the first through hole of the core substrate; and a second through-hole conductor comprising a metal film formed in the second through hole of the magnetic resin, wherein the magnetic resin includes a resin material and magnetic particles such that the metal film of the second through-hole conductor is in contact with the magnetic particles.
 2. The inductor built-in substrate according to claim 1, wherein the core substrate includes a core material, inorganic particles, and a resin material, and the magnetic resin does not contain a core material.
 3. The inductor built-in substrate according to claim 1, wherein no metal film is formed on an inner wall of the opening of the core substrate.
 4. The inductor built-in substrate according to claim 1, wherein the magnetic resin is formed such that the magnetic particles have an average particle size in a range of 5 μm to 45 μm.
 5. The inductor built-in substrate according to claim 1, wherein the magnetic resin comprises iron oxide filler.
 6. The inductor built-in substrate according to claim 2, wherein no metal film is formed on an inner wall of the opening of the core substrate.
 7. The inductor built-in substrate according to claim 2, wherein the magnetic resin is formed such that the magnetic particles have an average particle size in a range of 5 μm to 45 μm.
 8. The inductor built-in substrate according to claim 2, wherein the magnetic resin comprises iron oxide filler.
 9. The inductor built-in substrate according to claim 3, wherein the magnetic resin is formed such that the magnetic particles have an average particle size in a range of 5 μm to 45 μm.
 10. The inductor built-in substrate according to claim 3, wherein the magnetic resin comprises iron oxide filler.
 11. The inductor built-in substrate according to claim 4, wherein the magnetic resin comprises iron oxide filler.
 12. The inductor built-in substrate according to claim 6, wherein the magnetic resin is formed such that the magnetic particles have an average particle size in a range of 5 μm to 45 μm.
 13. The inductor built-in substrate according to claim 6, wherein the magnetic resin comprises iron oxide filler.
 14. The inductor built-in substrate according to claim 1, wherein the magnetic resin is formed such that the magnetic particles in the magnetic resin have cut surfaces exposed on a wall surface of the second through hole and that the metal film of the second through-hole conductor is in contact with the cut surfaces of the magnetic particles.
 15. The inductor built-in substrate according to claim 1, wherein the core substrate includes a core material and a resin material, and the magnetic resin does not contain a core material.
 16. The inductor built-in substrate according to claim 1, wherein the core substrate includes a core material, inorganic particles, and a resin material.
 17. The inductor built-in substrate according to claim 1, wherein the magnetic resin does not contain a core material.
 18. A method for manufacturing an inductor built-in substrate, comprising: forming an opening in an insulating base material; filling a magnetic resin comprising magnetic particles in the opening formed in the insulating base material; curing the magnetic resin filled in the opening of the insulating base material; forming a first through hole in the insulating base material; forming a second through hole in the magnetic resin filled in the opening of the insulating base material; and forming a plating film in the first through hole formed in the insulating base material and a plating film in the second through hole formed in the magnetic resin filled in the opening of the insulating base material, wherein the forming of the second through hole in the magnetic resin includes cutting surfaces of the magnetic particles in the magnetic resin such that cut surfaces of the magnetic particles are exposed on a wall surface of the second through hole.
 19. The method for manufacturing an inductor built-in substrate according to claim 18, wherein the magnetic resin comprises iron oxide filler.
 20. The method for manufacturing an inductor built-in substrate according to claim 18, further comprising: applying desmear on the first through hole formed in the insulating base material and the second through hole formed in the magnetic resin filled in the opening of the insulating base material before the forming of the plating films such that the desmear is applied on the second through hole without using an acidic agent. 